The invention relates to an electro-optical module for transmitting and/or receiving optical signals on at least two optical data channels.
Modules for bidirectional optical data traffic operate, for example, in a star structure in such a manner that data streams are transmitted in opposite directionsxe2x80x94in the direction of a central feed point (upstream) and in the direction of further receivers (downstream)xe2x80x94in an optical fiber, in which case identical or different wavelengths can be used for the individual data channels. In particular, wavelength-division multiplexing methods are used in which light signals at a number of wavelengths are transmitted simultaneously on one optical fiber. There is thus a need for electro-optical modules having transmitting and receiving components which inject into an optical fiber, and output from it, signals for a number of optical data channels.
A module of this generic type is known from European Publication EP-A-238 977. This transmitting and receiving module for a bidirectional communications network uses free-beam optics in which spherical lenses are arranged at a distance from one another between a laser diode and the end of an optical fiber, and focus the laser light onto the end of the fiber. A wavelength-selective beam splitter is arranged between the spherical lenses, for wavelength separation, and separates light which is emitted from the end of the fiber and is at a wavelength different to the wavelength of the laser light from the beam path and passes it to a detector or receiving component.
A disadvantage of this known module is that the light is passed through free-beam areas. The lenses that are used thus act refractively, that is to say the refraction power acts only on the boundary surface between the lens and air. The presence of free-beam areas demands hermetic encapsulation of the module, in order to prevent condensation in the free-beam area. Furthermore, the known module must be mechanically very robust and insensitive to temperature fluctuations in order to ensure that the laser light is reliably injected into the optical fiber (the diameter of a single-mode optical fiber is generally only 9.3 mm). A final disadvantage of the known module is that an electrical connecting contact must be made on two different sides of the module. This involves increased installation complexity for the user.
International publication WO-A-96/00915 discloses a module for multiplexing/demultiplexing of optical signals, which forms a phased array grating on a substrate and is used both for separation and for combination of a number of optical channels. The waveguides are in the form of integrated optical waveguides. A disadvantage of this arrangement is that the transmitting and receiving components must be mounted on or attached to the substrate without being capped. The substrates are also relatively large, since the waveguides must be routed with large radii, and are correspondingly expensive. A further problem is that special structures are required in order to couple external optical waveguides to the substrate.
Furthermore, fully integrated bidirectional modules for transmitting and receiving optical signals are known, in which the waveguides, transmitting component and receiving component are integrated on a common semiconductor substrate mount. However, these modules are very expensive.
It is accordingly an object of the invention to provide an optical module which overcomes the above-mentioned disadvantageous of the prior art apparatus and methods of this general type. In particular, it is an object of the invention to provide an optical module based on a new module concept for transmitting and/or receiving optical signals, and which has a simple, compact and modular design and can be produced cost-effectively.
With the foregoing and other objects in view there is provided, in accordance with the invention an electro-optical module for transmitting and/or receiving light of a plurality of optical channels. The electro-optical module includes an optical waveguide with at least two optical waveguide sections each section having at least one inclined end surface. The inclined end surfaces of the optical waveguide sections are positioned axially one behind the other. Light is injected into or light is output from the optical waveguide for a specific optical data channel by light for the optical data channel being passed to an inclined end surface, or emerging from it, at an angle relative to the optical axis of the optical waveguide.
The solution according to the invention provides a physical concept which is based on using a type of optical xe2x80x9cT-piecexe2x80x9d in which the horizontal arm of the T is provided by mutually adjacent optical waveguide sections. Light is output/injected at right angles or transversely from/into the optical waveguides by inclined end surfaces of optical waveguide sections at which the light is emitted or injected transversely. Such an end surface in this case always has an associated transmitting or receiving component arranged essentially at right angles to the optical axis of the optical waveguide. Optical coupling is provided in such a way that the light which is deflected on an inclined end surface passes through the sheath of the optical waveguide section (and adjacent materials) and is then coupled essentially by a free beam to the optically active area of the transmitting or receiving component, or vice versa.
The invention provides closed wave guidance in a transparent medium which essentially requires no free-beam optics for injecting light into and outputting light from the optical waveguide. The stability with regard to thermal and mechanical loads is in this case very high because of the closed wave guidance and because of the lack of optics which increase errors. A further advantage is that no wavelength-selective elements, which need to be installed separately, are required since the inclined end surfaces of the optical waveguide segments are used as mounts for these waveguide-selective elements.
Another advantage is that the solution according to the invention allows the optical waveguide to be routed close to the transmitting or receiving component, which can be connected directly to a holder for the optical waveguide, and that the electrical connections of the module are located on one side of the module. The latter facilitates simple installation.
In accordance with an added feature of the invention, at least one end surface of the optical waveguide sections is coated with a wavelength-selective filter. This allows use for wavelength division multiplexing, in which light signals at different wavelengths are transmitted on the optical waveguide. One wavelength is output via each wavelength-selective filter applied to the end surface, while that end surface is transparent to any other wavelength or wavelengths.
In accordance with an additional feature of the invention, the end surfaces of two adjacent optical waveguide sections are coplanar. This means that the two end surfaces of adjacent optical waveguide sections are immediately adjacent to one another with as little gap as possible in the joint so that scarcely any losses arise due to reflections between the two end surfaces. The angle of the end surfaces to the optical axis of the optical waveguide is essentially 45xc2x0. The term xe2x80x9cessentiallyxe2x80x9d in this case means that there may also be deviations from this value (of up to 20xc2x0) in order to avoid feedback, for example. The only essential feature is that the injected or output light is deflected sufficiently by the inclined end surface.
In accordance with another feature of the invention, the optical waveguide sections are each arranged in a glass ferrule which is transparent for light at the wavelengths used and which has an end surface inclined in a corresponding manner to the optical waveguide sections at its ends. The deflective light in this case first of all passes through the sheath of the optical waveguide section, and then through the glass ferrule, and vice versa. The glass ferrules ensure that the optical waveguide sections are held and guided reliably.
In accordance with a further feature of the invention, there is provided, a mounting tube which accommodates the individual glass ferrules and the optical waveguide sections arranged in them, and positions them axially with respect to one another. The mounting tube preferably has a longitudinal slot and at the same time surrounds the glass ferrules in a spring manner. This allows tolerances in the internal diameter of the tube to be compensated for by the spring effect so that the only significant tolerances are those of the glass ferrule external diameter.
The use of a mounting tube to accommodate the glass ferrules in a spring manner and having a longitudinal slot also simplifies the installation of the optical waveguide sections and of the associated glass ferrules. When the glass ferrule sections are being introduced, it is desirable for them to be arranged in rows on their inclined end surfaces with as little gap at the joint as possible. Easily handled matching, without any clearance, between the outer surface of the ferrule and the inside of the mounting tube means that the inclined end surfaces can be located against one another essentially without any clearance simply by pressing the individual ferrules against one another, with any position that has been attained being maintained by virtue of the spring arrangement in the mounting tube and the force on the individual ferrules resulting from this. In the process, any lack of coplanarity of the end surfaces is overcome by axial pressure on the individual ferrules, which leads to the individual ferrules being rotated about the common axis, until coplanarity is achieved.
In accordance with a further added feature of the invention, an immersion means that fills any gap which is still present between the end surfaces of mutually adjacent optical waveguide sections. The immersion means has a matched refractive index. To this end, the invention preferably provides for a radial opening for insertion of the immersion means to be formed in the mounting tube in the region of each of the mutually adjacent optical waveguide sections or glass ferrules.
In accordance with a further additional feature of the invention, fixing means for fixing the mounting tube on a holder are preferably formed on the mounting tube. These fixing means are, in particular, longitudinal grooves.
In accordance with yet another feature of the invention, a number of transmitting or receiving components are arranged one behind the other in the module in the direction of the optical axis of the optical waveguide or of the optical waveguide sections. Each of the transmitting or receiving components is associated with an inclined end surface of an optical waveguide section. The module according to the invention in this case has the characteristics of a kit, since different transmitting or receiving elements can be arranged one behind the other as required and can thus be added to in particular to form a multiplexing/demultiplexing arrangement in which any desired number of transmitting and/or receiving components are arranged one behind the other. The end surfaces of the individual optical waveguide sections are in this case coated with wavelength-selective filters for different wavelengths, so that one data channel is in each case input or output on each boundary area between two adjacent optical waveguide sections.
The optical axis of a transmitting or receiving component in this case always runs (assuming that the end surface of the associated optical waveguide receiving is inclined at 45xc2x0) essentially at right angles to the optical axis of the optical waveguide section. xe2x80x9cEssentially at right anglesxe2x80x9d in this case means that this may be an angle which allows the light falling on the end surface of the optical waveguide section to be deflected into the optical waveguide section, and vice versa.
In accordance with yet an added feature of the invention, the transmitting or receiving components are each arranged in a TO can. The TO cans are standard containers, known from the prior art, for optical transmitting or receiving modules, whose form is similar to the pack of a xe2x80x9cclassicalxe2x80x9d transistor, but which have a glass window for light to enter and emerge from on the upper face. The module according to the invention in this case preferably has a mounting pack associated with each TO can, which firstly accommodates the TO can and secondly has a mounting cap for accommodating and holding the mounting tube. The pack in this case has a window through which light can pass, or is composed of a translucent material, in order to avoid interfering with the beam path between the end surface of the respective optical waveguide section and the transmitting or receiving component.
The transmitting or receiving component may, however, also be arranged other than in a TO can, for example in a semiconductor pack which can be mounted on a printed circuit board. The mounting tube is then mounted on one side of the semiconductor pack.
In accordance with yet an additional feature of the invention, a lens for beam focusing is arranged in each beam path between an end surface of an optical waveguide section and the associated transmitting or receiving component. If the transmitting or receiving component is located very close to the associated optical waveguide section, it may, however, be possible to dispense with the lens optics as well.
In accordance with yet a further feature of the invention, the optical waveguide core becomes larger from a first optical waveguide section to an adjacent optical waveguide section. This is of particular interest when the light passing through the end surface of that optical waveguide section which has the enlarged core is intended to be imaged on a receiver having an enlarged light-sensitive layer.
The optical waveguide, or each of the individual optical waveguide sections, is preferably a single-mode waveguide. However, the modular concept of the invention means that different waveguide types may also be combined with one another, for example single-mode fibers and multimode fibers. In principle, it is also possible to use only multimode fibers.
It should be mentioned that the use of different wavelengths for transmitting data for a number of data channels is admittedly preferable, but is not absolutely essential. If only one wavelength is used, for example, different data channels can be provided by different coding or by different time windows. In this case, the adjacent end surfaces of two optical waveguide sections form, for example, a 50/50 beam splitter which ensures that light is in each case passed to the transmitting or receiving component. The data for a specific data channel are in this case determined in an evaluation unit.
In accordance with a concomitant feature of the invention, light at a specific wavelength can be selected not directly at the inclined end surfaces, but rather before or after them, for example in a filter associated with the receiving component.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in electro-optical module for transmitting and/or receiving optical signals on at least two optical data channels, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will he best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in electro-optical module for transmitting and/or receiving optical signals on at least two optical data channels, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.